A nano-sized circular ring structure demonstrates important application prospects in the semiconductor field. For example, for a solar cell of vertical structure, the circular ring structure can absorb photo-generated carriers more effectively than a columnar structure, thus improving efficiency of the cell. In a field of LED, researchers usually increase the light-emission efficiency by employing a pattern substrate technology, and as compared with a typical sapphire pattern substrate of columnar structure, a pattern substrate of circular ring structure can increase the light reflection more effectively, and it is hopeful to enable the LED obtain higher light-emission efficiency.
Due to the limitation by the minimum line width of optical lithography, it is very difficult to fabricate the nano-sized circular ring structure by a conventional optical lithography. The fabrication of the nano-sized circular ring often depends on advanced and expensive processing technologies such as the electron beam lithography, the focusing ion beam lithography etc., which certainly increases the product fabrication cost. Of course, the nano-sized circular ring structure may be self-assembly fabricated based on a chemical growth technology, such as a growth mechanism based on Vapor-Liquid-Solid. However, it is difficult to ensure consistency and uniformity of the nano structure by using the self-assembly technology. Moreover, as compared with nanowire fabrication, the technology for self-assembly fabricating a nano-sized circular ring structure is less mature.